Heat oven to 350°. Season beef with salt and pepper. Heat oil in a Dutch oven on high; brown beef on all sides, about 3 to 5 minutes. Reduce heat to medium-high, add carrots, onions and garlic; cook for 2 minutes. Stir in flour and cook 1 minute. Add wine, stock, tomato paste and rosemary and bring to a boil. Cover, place in oven and braise at 350° for 11/2 hours or until meat is knife-tender and sauce thickens.
Meanwhile, place celery root, potatoes and garlic in a lidded pot, covering with cold water. Bring to a boil, reduce heat to medium, and simmer, covered, until vegetables are tender, 25 to 30 minutes. Drain; puree in blender or processor with milk until smooth. (Add more milk if necessary.) Season with salt.
Serve braised beef and sauce on top of the celery root puree. Garnish with chopped parsley, if desired.